LTC6911CMS-2 datasheet(13/20 Pages) LINER

13 / 20 page

LTC6911-1/LTC6911-2

sn691112 691112fs

AGND (Pin 2): Analog Ground. The AGND pin is at the

midpoint of an internal resistive voltage divider, develop-

ing a potential halfway between the V+ and V– pins, with an

equivalent series resistance to the pin of nominally 5k

Ω

(Figure 1). AGND is also the noninverting input to both the

internal channel A and channel B amplifiers. This makes

AGND the ground reference voltage for the INA, INB, OUTA

and OUTB pins. Recommended analog ground plane con-

nection depends on how power is applied to the LTC6911-X

(see Figures 2, 3 and 4). Single power supply applications

typically use V– for the system signal ground. The analog

ground plane in single supply applications should there-

fore tie to V–, and the AGND pin should be bypassed to this

ground plane by a high quality capacitor of at least 1

µF

(Figure 2). The AGND pin provides an internal analog

reference voltage at half the V+ supply voltage. Dual supply

applications with symmetrical supplies (such as

±5V)

have a natural system ground plane potential of zero volts,

which can be tied directly to the AGND pin, making the zero

volt ground plane the input and output reference voltage

for the LTC6911-X (Figure 3). Finally, if dual asymmetrical

power supplies are used, the supply ground is still the

natural ground plane voltage. To maximize signal swing

PI FU CTIO S

capability with an asymmetrical supply, however, it is

often desirable to refer the LTC6911-X’s analog input and

output to a voltage equidistant from the two supply rails V+

and V–. The AGND pin will provide such a potential when

open-circuited and bypassed with a capacitor (Figure 4).

Figure 3. Dual Supply Ground Plane Connection

Figure 2. Single Supply Ground Plane Connection

LTC6911-X

DIGITAL GROUND PLANE

(IF ANY)

ANALOG

GROUND

PLANE

SINGLE-POINT

SYSTEM GROUND

691112 F03

0.1

µF

V–

V+

0.1

µF

Figure 4. Asymmetrical Dual Supply Ground Plane Connection

LTC6911-X

DIGITAL GROUND PLANE

(IF ANY)

ANALOG

GROUND

PLANE

SINGLE-POINT

SYSTEM GROUND

691112 F04

0.1

µF

V–

V+

0.1

µF

≥1µF

REFERENCE

V+ + V–

DIGITAL GROUND PLANE

(IF ANY)

ANALOG

GROUND

PLANE

SINGLE-POINT

SYSTEM GROUND

REFERENCE

V+

691112 F02

≥1µF

LTC6911-X

V+

0.1

µF

LTC6911CMS-2 Datasheet(PDF) 13 Page - Linear Technology

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